M. Ahmadi et al. / Journal of Molecular Catalysis A: Chemical 386 (2014) 14–19
15
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3
30 C in different environments (H2 or N ) in the gas phase and
We report the catalytic decarboxylation of oleic acid and fur-
ther conversion of the resulting product linear paraffins over
bifunctional Pt/SAPO-11 and Pt–acidic, chloride, alumina catalysts
in a single process stage. The direct, single stage conversion of
fatty acids to branched and aromatic hydrocarbons (especially, the
industrially important dodecylbenzene) over a single, bi-functional
catalyst has not, so far, been reported.
2
found that the presence of hydrogen is desirable to maintain stable
catalytic activity during the decarboxylation reaction although the
role of hydrogen is not apparent from the stoichiometry of the
decarboxylation reaction. In contrast, no reaction occurred in a
nitrogen atmosphere. Snare et al. [8] conducted liquid phase deoxy-
genation experiments in a continuous flow reactor under Ar and
H2 atmosphere and solvent-free conditions using a Pd/C catalyst.
The formation of hydrocarbons, mainly olefins and aromatics, were
below 10 mol%. Representative examples of catalysts employed
for the conversion of stearic acid to heptadecane include selenium
2. Experimental
2.1. Catalyst preparation and characterization
[
18], complexes of Pd and Rh [19], and Pd–C [20]. However, in these
studies, the yield to heptadecane or stearic acid conversion was low.
Research related to the conversion of saturated fatty acids, such as
stearic acid, to straight chain hydrocarbon is well-documented [21].
Some studies of the decarboxylation of the unsaturated oleic acid
have also been reported [8,22–25]. In most of the above studies, the
support for the metal has been catalytically inert material (like car-
bon) or relatively, non-acidic components, like silica or non-acidic
alumina. The influence of stronger acidic supports in modifying the
carbon skeleton of the linear C16–C18 paraffins (initial products of
the decarboxylation of the fatty acid), by isomerization, cracking,
cyclisation, hydrocracking etc., had not been explored.
Biodiesels, fatty acid methyl esters (FAME) are produced from
vegetable oils or triglycerides of other biological origin by trans-
esterification with alcohols (generally methanol) and are mainly
used as renewable diesel fuel components. But these have sev-
eral disadvantages e.g. high pour points, depositions in the fuel
system and the combustion chamber; lower storage stability (oxi-
dation and heat degradation) because of the olefinic double bonds;
aptitude to water intake and hydrolysis sensitivity of the ester
bonds, which generates corrosive acids. Consequently, in the EU
the maximum blending quantity of the fatty acid methyl esters is
limited to 7.0 v/v% according to EN 59 0:2009 standard. To satisfy
the application requirements of the diesel vehicles hydrocarbons
with different conformation (paraffin mixtures) should be pro-
duced from triglycerides and fatty acids. As these normal paraffin
5 wt% Pt/SAPO-11 catalysts were prepared by conventional dry
impregnation of SAPO-11 samples with platinum nitrate solutions.
Similarly, 5 wt% Pt–alumina was prepared by dry impregnation
of acidic, chlorided alumina with platinum nitrate solution. The
catalysts, both fresh and spent, were characterized by X-ray diffrac-
tion (XRD), nitrogen adsorption (BET) and transmission electron
microscopy (TEM). XRD patterns were collected on a Bruker D8
Discover diffractometer at 40 kV and 40 mA with Cu K␣ radiation.
BET surface areas and N2 adsorption–desorption isotherms were
collected in a Micromeritics Tristar-3000 porosimeter at 77 K using
liquid nitrogen as coolant. Before measurements, the catalyst was
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degassed at 150 C for 3 h. Transmission electron microscopy (TEM)
was used to inspect the morphology of Pt/SAPO 11. TEM images
were taken on Technai F20 FEI TEM using a field emission gun,
operating with an accelerating voltage of 200 kV.
2.2. Reaction procedure
Oleic acid (90%, Alfa-Aesar) was used as the unsaturated fatty
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acid. Pt/SAPO-11 was pre-activated in the oven for 3 h at 150 C.
The decarboxylation reactions were conducted in a 250 ml stainless
steel, high pressure autoclave batch reactor (Parr model 4576A).
Oleic acid and Pt/SAPO-11 were loaded into the reactor with a mass
ratio of 18:1. Before the reaction started, the air in the reactor was
removed by flushing with CO or H . The pressure was increased to
2
2
(
mainly n-C12 to n-C-20) mixtures have high cetane number, they
the desired reaction pressure (usually 20 bar). Under constant stir-
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have excellent performance. On the other hand, the pour point of
these paraffin mixtures is high so their structure should be modi-
ring conditions, the reactor was heated at a rate of 10 C/min to the
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reaction temperature (200–325 C) and this temperature was kept
fied to fulfill the requirements of the diesel blending components
constant during the reaction. Reaction of oleic acid with Pt–alumina
was carried out in a similar manner. After the reaction, the catalyst
particles were separated, by filtration, from the liquid product and
washed with acetone for further characterization.
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(
the pour point should be below 5 C). For this purpose the catalytic
isomerization of the normal to isoparaffins is, often, used to lower
their pour points [26,27].
Hydroisomerization reactions of normal paraffins are carried
out in the presence of the bi-functional catalysts. The degree of
isomerization, the product yield and composition are significantly
affected by the properties of the used catalyst (acidity, surface
area and pore size distribution), the applied operational parame-
ters (temperature and pressure). Isomerization takes place in high
degree in the presence of different noble metal (such as Pd and
Pt) containing zeolites (ZSM-5, ZSM-22), mesoporous structures
2.3. Product analysis
The liquid phase product withdrawn from the reactor was ana-
lyzed with a gas chromatograph (GC, 7820 A) equipped with a
HP-5 MS column (with dimensions of 30 m × 250 m × 0.25 m)
and a 5975 MSD detector. Samples were silylated with N,O-
bis(trimethyl)-trifloroacetamide, BSTFA (Acros organics, 98%)
before the GC analysis. After addition of the silylation agent, the
(
MCM-41, Al-MCM-41) and silica-alumina-phosphates (SAPO-11,
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SAPO-31, SAPO-41) as they have mild acidity [27]. Some catalysts
like SAPO-11, SAPO-31, SAPO-41 were found to be favorable for the
isomerization of long chain paraffins [29]. Isomerization of paraf-
fins over Pt–SAPO-11, Pd–SAPO-11, Pt–SAPO-5 have been reported
in the literature [27–31].
If the deoxygenation of the fatty acid and subsequent isomer-
ization/hydrocracking of the resulting C17–C18 linear paraffins to
branched, gasoline-range C5–C10 hydrocarbons with lower pour
points and higher octane numbers can be accomplished by a
bifunctional catalyst in a single reactor, it will represent a signifi-
cant advance in the process of conversion of lipid biomass material
to ‘drop-in’ hydrocarbon transport fuels, like motor and aviation
gasoline.
samples were kept at 60 C for 1 h. A sample of 0.2 L was injected
into the GC column (225 C, 10.5 psi) with a split ratio 20:1, and the
carrier gas (helium) flow rate was 1 mL/min. The following tem-
perature program of the gas chromatograph was used for analysis:
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100 C for 5 min, 300 C (20 C/min, for 2 min). Quantitative anal-
ysis was accomplished by generating and using calibration curves
for each compound of interest. The product identification was con-
firmed with a gas chromatograph–mass spectrometer (GC–MS).
The decarboxylation conversion of the oleic acid was estimated
from the reduction in the number of oleic acid carboxylic acid
groups during the reaction. The amount of carboxylic acid groups
remaining in the products after the reaction was evaluated by quan-
tifying the acid number (ASTMD974). Acid number is the mass of
Ahmadi, Masoudeh
